Utility distribution fault restoration system

ABSTRACT

A power restoration system comprising a feeder, a plurality of power sources available to provide power to the feeder, a plurality of normally closed reclosing devices electrically coupled along the feeder, at least one normally open recloser electrically coupled to the feeder, and a plurality of normally closed switches electrically coupled along the feeder between each adjacent pairs of normally closed reclosing devices. Each switch is assigned a position code having a value for each of the plurality of power sources that determines when the switch will open in response to the fault current and which power source the switch is currently receiving power from, where timing control between the reclosing devices and the switches allows the switch to be selectively opened to isolate the fault within a single feeder section between each pair of adjacent switches or between each switch and a reclosing device.

BACKGROUND Field

The present disclosure relates generally to a fault restoration systemfor restoring power in an electrical power distribution network to asmany feeder segments as possible in response to a fault and, moreparticularly, to a fault restoration system for restoring power in anelectrical power distribution network to as many feeder segments aspossible in response to a fault.

Discussion of the Related Art

An electrical power distribution network, often referred to as anelectrical grid, typically includes a number of power generation plantseach having a number of power generators, such as gas turbines, nuclearreactors, coal-fired generators, hydro-electric dams, etc. The powerplants provide power at a variety of medium voltages that are thenstepped up by transformers to a high voltage AC signal to be connectedto high voltage transmission lines that deliver electrical power to anumber of substations typically located within a community, where thevoltage is stepped down to a medium voltage for distribution. Thesubstations provide the medium voltage power to a number of three-phasefeeders including three single-phase feeder lines that carry the samecurrent, but are 120° apart in phase. A number of three-phase and singlephase lateral lines are tapped off of the feeder that provide the mediumvoltage to various distribution transformers, where the voltage isstepped down to a low voltage and is provided to a number of loads, suchas homes, businesses, etc.

Periodically, faults occur in the distribution network as a result ofvarious things, such as animals touching the lines, lightning strikes,tree branches falling on the lines, vehicle collisions with utilitypoles, etc. Faults may create a short-circuit that increases the load onthe network, which may cause the current flow from the substation tosignificantly increase, for example, many times above the normalcurrent, along the fault path. This amount of current causes theelectrical lines to significantly heat up and possibly melt, and alsocould cause mechanical damage to various components in the substationand in the network.

Many times the fault will be a temporary or intermittent fault asopposed to a permanent or bolted fault, where the thing that caused thefault is removed a short time after the fault occurs, for example, alightning strike, where the distribution network will almost immediatelybegin operating normally. Permanent faults need to be cleared so thatelectrical power can be restored to the section of the networkexperiencing the service outage. Temporary faults often need to beaddressed to prevent the root cause of the fault from escalating into apermanent fault as well as increase the power quality and prevent wearon the equipment. This typically requires a field crew to identify thelocation of the fault and then make the repairs. Permanent faults can beeventually found by the field crew, however, the time it takes to findthe fault can be considerable. Temporary faults are often very difficultto find, and utility companies may decide to ignore such faults untilthey escalate into permanent faults.

Fault interrupters, such as reclosers, are provided on utility poles andin underground circuits along a feeder and have a switch to allow orprevent power flow downstream of the recloser. These reclosers detectthe current and voltage on the feeder to monitor current flow and lookfor problems with the network circuit, such as detecting a fault. Iffault current is detected the recloser is opened in response thereto,and then after a short delay closed. If fault current flows when therecloser is closed, it is immediately opened. If the fault current isdetected again or two more times during subsequent opening and closingoperations, then the recloser remains open, where the time between testsmay increase after each test. Reclosers are known that use pulse testingtechnologies to determine if the fault is still present without applyingthe full fault current to the network.

When a fault is detected, it is desirable that the first faultinterrupter upstream from the fault be opened as soon as possible sothat the fault is quickly removed from the network to prevent damage toequipment, personal injury, fires, etc., and so that the loads upstreamof that fault interrupter are not disconnected from the power source andservice is not interrupted to them. It is further desirable that if thefirst fault interrupter upstream from the fault does not open forwhatever reason, then a next fault interrupter upstream from the faultis opened, and so on. In order to accomplish this, it is necessary thatsome type of communications or coordination protection scheme beemployed in the network so that the desired fault interrupter is openedin response to the fault.

One known protection scheme for this purpose is referred to in the artas a time-current characteristic (TCC) coordination scheme. Generally,for a TCC coordination scheme each fault interrupter in a particularseries of fault interrupters on a feeder line is assigned a sliding TCCvalue that defines how fast the fault interrupter will open in responseto detecting a fault, where the TCC value is slower for lower currentsand is faster for higher currents, and where the sliding value defines aTCC curve. TCC curves with sliding values are typically used in systemswhere protection consists of both fuses and relayed fault interrupters.In systems without fuses a definite-time TCC is more commonly used. Asthe fault interrupters are provided farther downstream from the source,they are given faster TCC values so that the first upstream faultinterrupter from a detected fault will open before a next up streamfault interrupter from the fault, where the particular fault interrupterwill stop timing to its TCC value once a downstream fault interrupteropens and the fault is removed. However, traditional TCC coordinationschemes are limited in the number of fault interrupters a feeder linecan have because the TCC values cannot be too close together in orderfor the coordination to be effective. In other words, the number of TCCcurves that realistically can be provided is limited. Moreover, faultinterrupters closer to the source need to operate relatively slowly.

Another known protection scheme is referred to in the art as acommunication enhanced coordination (CEC) protection scheme, where allof the fault interrupters on the feeder are assigned the same initialTCC curve or definite time response. The CEC scheme includes sendingmessages between the fault interrupters on the feeder, where if acertain fault interrupter detects a fault it will send a message to allupstream fault interrupters identifying the fault and stating that thefault is downstream of the sending fault interrupter. When this occurs,the upstream fault interrupters will shift their TCC curves or definitetime response to be longer so that they don't open at the same time asthe sending fault interrupter, but will open if the sending faultinterrupter doesn't open after its TCC curve or definite time responseexpires. Therefore, the most downstream fault interrupter that isimmediately upstream of the fault will not receive a fault message froma further downstream fault interrupter because the further downstreamfault interrupter does not detect a fault, and thus the faultinterrupter that is immediately upstream of the fault will be the one toopen first because it is operating on its initial TCC curve or definitetime response. If for some reason that fault interrupter does not open,the upstream fault interrupters will then open using the fault detectionmessage and now operating on the longer TCC curve or definite timeresponse. These types of CEC protection schemes do not have thelimitations of the traditional TCC schemes referred to above, but theirspeed may still be limited by the performance of the communicationmethod.

Sections of the feeder that lose power that are downstream of a faultedfeeder section, i.e., sections of the feeder between reclosers, and haveno fault can have power service restored using a second source, where anormally open recloser would prevent the second source from providingpower to the feeder during normal operation. If this networkconfiguration only includes one feeder having sources at both ends,where one of the sources is isolated with a normally open switch, thenit is relatively straightforward to isolate the feeder section havingthe fault and provide power from both sources at opposite ends of thefeeder. However, if there are multiple sources and multipleinterconnected feeders, switch coordination is much more complex toisolate the fault to only the feeder section that is faulted. Thus, inthese network configurations some type of communications systems isgenerally required to pass information between devices to identify thefault location and then restore unfaulted sections. However, these typesof communications systems that may employ wireless communicationsschemes are only as reliable as the communications scheme itself.

SUMMARY

The following discussion discloses and describes a fault restorationsystem for restoring power in an electrical power distribution networkto as many feeder segments as possible in response to a fault, where thesystem does not require communications between the devices. In onenon-limiting embodiment, the power restoration system includes a firstfeeder having a first end and a second end, a first power sourceavailable to provide power to the first feeder at its first end, and asecond power source available to provide power to the first feeder atits second end. The system also includes a first normally closedreclosing device provided in the first feeder adjacent, for example, tothe first power source and allowing the first power source to providepower to the first feeder during normal operation, and a first normallyopen reclosing device provided in the first feeder adjacent, forexample, to the second power source and allowing the second power sourceto provide power to the first feeder during power restorationconditions. The system further includes a second feeder having a firstend and a second end coupled to the first feeder, a third power sourceavailable to provide power to the second feeder at its first end, and asecond normally open reclosing device provided in the second feederadjacent, for example, to the third power source and allowing the thirdpower source to provide power to the second feeder during powerrestoration conditions. The system also includes at least second andthird normally closed reclosing devices provided along the first feederbetween the first and second normally closed reclosing devices andallowing the first power source to provide power to the first feederdownstream of the normally closed reclosing device during normaloperation, where each of the normally closed and normally open reclosingdevice include an interrupter and one or more current and voltagesensors for measuring current on the feeder and measuring voltage on thefeeder at both sides of the reclosing device, and where each normallyclosed reclosing device detects fault current and opens its interrupterin response to fault current and where the normally closed reclosingdevices are coordinated with each other to open in response to faultcurrent depending on its location along the first feeder. The systemfurther includes a plurality of normally closed switches electricallycoupled along the first and second feeders between each adjacent pair ofnormally closed reclosing devices, each switch including one or morecurrent and voltage sensors for measuring current on the first or secondfeeder and measuring voltage on the first or second feeder at both sidesof the switch, where each switch is assigned a position code having avalue for each of the first, second and third power sources thatdetermines when the switch will open in response to the fault currentand which power source the switch is currently receiving power from, andwhere timing control between reclosing devices and the switches allowsthe switch to be selectively opened to isolate the fault within a singlefeeder section between each pair of adjacent switches or between eachswitch and a reclosing device.

Additional features of the disclosure will become apparent from thefollowing description and appended claims, taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified schematic illustration of an electrical powerdistribution network showing a power restoration system includingreclosers and switches;

FIG. 2 is a simplified illustration of a recloser in the electricalpower distribution network shown in FIG. 1;

FIG. 3 is a simplified illustration of a switch in the electrical powerdistribution network shown in FIG. 1;

FIG. 4 is a state diagram for the normally closed reclosers in thenetwork shown in FIG. 1 for a power restoration process;

FIG. 5 is a state diagram for the normally open reclosers in the networkshown in FIG. 1 for the power restoration process;

FIG. 6 is a state diagram for the normally closed switches in thenetwork shown in FIG. 1 for the power restoration process;

FIG. 7 is the schematic illustration of the electrical powerdistribution network shown in FIG. 1 with switches opened to isolate afault; and

FIG. 8 is a state diagram for the normally closed reclosers in thenetwork that is similar to the state diagram shown in FIG. 4 for anotherembodiment.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The following discussion of the embodiments of the disclosure directedto a power restoration system for restoring power to as many feedersections as possible in an electrical power distribution network inresponse to a fault, where the system does not require communications,is merely exemplary in nature, and is in no way intended to limit theinvention or its applications or uses.

This disclosure proposes a power restoration system that does not relyon communications between reclosers and other switching devices. Thepower restoration system employs a combination of reclosers and a set ofthree switches between adjacent reclosers, where both the switches andthe reclosers are used to isolate the faulted section of the feeder. Ingeneral, for a first embodiment, the system works using a recloserclosest to a fault as the device that clears the initial fault, thentests for a permanent fault using reclosing or pulse testing techniques.If the fault is downstream of the recloser and downstream of a switch inthe section, the switch closest to the fault that senses fault currentwill open using fault counts and the timing of the recloser pulsesequence. After a normally closed recloser disconnects the fault fromthe normally closed side, often using a switch, the normally openrecloser will begin its restoration with a delay that allows thenormally closed recloser to finish. Then, the normally open recloserwill test for a fault, and if it finds no fault, it will close. The nextrecloser will then detect good voltage on one side and after a delaywill test for a fault. When a fault is detected, reclosing or pulsetesting will determine if the fault still exists and allow a switch toisolate the fault, then it will restore the remaining distributionsystem. If the fault clears at any time, the system will stop testingand close the recloser that was doing the testing.

If a second fault occurs, the recloser will open to clear the fault, andbegin testing. A switch or recloser adjacent to the fault will open. Ifthere is a possibility of power from the other side of the faulted linesection, another recloser will test the line and find the other side ofthe second fault and the adjacent switch will open.

In a second embodiment, the power restoration system uses the same TCCcurve in the reclosers for both the first and second faults so all ofthe reclosers that are exposed to the fault current will open. Thisresults in a higher momentary average interruption frequency index(MAIFI) than the embodiment that uses TCC curves coordinated for theoriginal fault only, and the embodiment that will have coordinated TCCcurves in both directions. The advantage of this embodiment is that itis simple to configure as each recloser is configured with the same TCCcurve.

In a third embodiment, the power restoration system uses a different setof TCC curves for the second fault so that only the recloser closest tothe second fault will open. This results in a lower MAIFI than theembodiment that only uses TCC curves coordinated for the original fault,or the method that uses all of the same TCC curves.

Some terminology as used herein is defined as follows. An arm pulseoccurs when a switch or recloser sees a fault of a duration thatcorresponds with a very fast opening of a recloser. Fast close/opentests are several cycle over current events and are the shortestnon-pulse close operation. For a “condition is not true” state, a switchwill evaluate which upstream device is testing based on a run timer,where if the set of pulses and the pulse number for the switch to openare not the same, the condition is not true. For a “condition is true”state, a switch will evaluate which upstream device is testing based onthe run timer. If the set of pulses and the pulse number for the switchto open are the same, the condition is true. A double zero conditionoccurs if the voltage sensors on both sides of a recloser is below 5%and a no voltage sag condition occurs if the voltages are over 75%.

FIG. 1 is a schematic type diagram of an electrical power distributionnetwork 10 that employs a power restoration system and method asdescribed herein. The network 10 includes three AC power sources 12, 14and 16, such as electrical substations that step down high voltage powerfrom a high voltage power line (not shown) to a medium voltage powerline. The power sources 12 and 14 are at opposite ends of a three-phasefeeder 18 and the power source 16 is at an end of a three-phase feeder20 opposite to where the feeder 20 is tapped off of the feeder 18. Thenetwork 10 includes a normally closed recloser (NCR) 24 adjacent to thesource 12, a normally open recloser (NOR) 26 adjacent to the source 14,a normally open recloser 28 adjacent to the source 16 and two normallyclosed reclosers 30 and 32 on the feeder 18 between the reclosers 24 and26. Because the reclosers 24, 30 and 32 are normally closed and thereclosers 26 and 28 are normally open, all of the loads (not shown)along the feeders 18 and 20 are serviced by the source 12 during normaloperation. Three switches 34, 36 and 38 are provided along the feeder 18between the reclosers 24 and 30, three switches 40, 42 and 44 areprovided along the feeder 18 between the reclosers 30 and 32, threeswitches 46, 48 and 50 are provided along the feeder 18 between thereclosers 32 and 26, and a switch 52 is provided on the feeder 20between the recloser 28 and the location where the feeder 20 is tappedoff of the feeder 18 between the switches 40 and 42. The reclosers 24-32and the switches 34-52 would all likely be mounted on utility poles,where the span length between adjacent reclosers 24-32 is typicallymiles.

The feeders 18 and 20 have a number of feeder segments between adjacentdevices in the network 10, such as the sources 12, 14 and 16, thereclosers 24-32 and the switches 34-52. In this example, a feedersegment 60 is provided and defined between the source 12 and therecloser 24, a feeder segment 62 is provided and defined between thesource 14 and the recloser 26, a feeder segment 64 is provided anddefined between the source 16 and the recloser 28, a feeder segment 66is provided and defined between the recloser 24 and the switch 34, afeeder segment 68 is provided and defined between the switches 34 and36, a feeder segment 70 is defined between the switches 36 and 38, afeeder segment 72 is defined between the switch 38 and the recloser 30,a feeder segment 74 is defined between the recloser 30 and the switch40, a feeder segment 76 is defined between the switches 40, 42 and 22,which is the tap location of the feeder 20, a feeder segment 78 isdefined between the switches 42 and 44, a feeder segment 80 is providedand defined between the switch 44 and the recloser 32, a feeder segment82 is provided and defined between the recloser 32 and the switch 46, afeeder segment 84 is provided and defined between the switches 46 and48, a feeder segment 86 is defined between the switches 48 and 50, afeeder segment 88 is provided and defined between the switch 50 and therecloser 26, and a feeder segment 90 is provided and defined between therecloser 28 and the switch 52. It is noted that in the system 10 thenormally open reclosers 26 and 28 are place near the sources 14 and 16,respectively. However, this is merely for illustrative purposes in thatin a real system there would likely be many reclosers between alternatesources and any normally open reclosers.

The reclosers 24-32 and the switches 34-52 are all able to measurevoltage and current on the feeder 18 or 20, and the reclosers 24-32 areable to provide fault clearing as well as optionally using known testingtechniques, but the switches 34-52 are not able to provide faultclearing or testing. FIG. 2 is a simplified illustration of the recloser24 mounted on a utility pole 98 with the understanding that thereclosers 26-32 are the same or similar. The recloser 24 includes arelay or interrupter switch 100 for opening and closing the recloser 24to allow or prevent current flow therethrough on the feeder 18. Therecloser 24 also includes sensors 102 that are intended to represent oneor more current and voltage sensors for measuring the current andvoltage of the power signal propagating on the feeder 18 on one side ofthe switch 100, and voltage on both sides of the switch 100, acontroller 104 for processing the measurement signals and controllingthe position of the switch 100, and an optional transceiver 106 fortransmitting data and messages to a control facility (not shown) and/orto other reclosers, fault interrupters and components in the network 10.The configuration and operation of fault reclosers of this type are wellunderstood by those skilled in the art.

FIG. 3 is a simplified illustration of the switch 34 mounted on autility pole 110 with the understanding that the switches 36-52 are thesame or similar. The switch 34 includes an automatic open operator for aswitch 112 and a manual or automatic closing the switch 34 to allow orprevent current flow therethrough on the feeder 18. The switch 34 alsoincludes sensors 114 that are intended to represent one or more currentor voltage sensors for measuring the voltage of the power signalpropagating on the feeder 18 on both sides of the switch 112 and currenton one side of the switch 112, and a controller 116 for processing themeasurement signals and controlling the position of the switch 112,where the controller 116 includes a counter 118 for reasons that willbecome apparent from the discussion below.

The reclosers 24-32 can provide fault clearing and optionally testingusing known testing technologies as discussed above. In this design,each of the switches 34-52 is assigned a set of number values, and eachvalue determines when the switch 34-52 will open depending on which ofthe sources 12, 14 or 16 is providing the power in response to detectinga fault. Each time the switch 34-52 first detects fault current itbecomes armed. Each time the switch 34-52 detects fault current againduring the testing procedure it increments a counter, and when thecounter reaches the assigned value for the particular power source 12,14 or 16, the switch 34-52 opens. Therefore, each time one of thereclosers 24, 30 and 32 detects fault current it will open and close oroptionally pulse close thereafter to determine if the fault is stillpresent. Each switch 34-52 along the fault path will also detect thefault current when it initially occurs and each time the recloser 24-32closes or pulse closes if the fault is still present. By assigning ahigher value to the switch 34-52 closest to the recloser 24-32 and alower value to the switch 34-52 farthest from the recloser 24-32, thefarther switches 34-52 will open first, thus allowing the first switch34-52 upstream of the fault to open and limit the segments 60-90 of thefeeders 18 and 20 that are affected by the fault. The number of threeswitches between reclosers is selected because generally the number ofre-close or tests that are performed is four before the particularrecloser 24-32 is maintained open if the fault is still present.

Since there are three sources 12, 14 and 16 in the system 10, theswitches 24-32 are each assigned a three digit code where the positionof the digit in the code is the assigned value for each of the sources12, 14 and 16. For the power restoration system discussed herein, thefirst digit in the code is for when power is being supplied by thesource 12, the second digit in the code is for when power is beingsupplied by the source 14, and the third digit in the code is for whenpower is being supplied by the source 16. In this non-limiting example,the switch 34 is assigned code 311, the switch 36 is assigned code 222,the switch 38 is assigned code 133, the switch 40 is assigned code 311,the switch 42 is assigned code 222, the switch 44 is assigned code 131,the switch 46 is assigned code 313, the switch 48 is assigned code 222,the switch 50 is assigned code 131 and the switch 52 is assigned code113.

FIG. 4 is a state diagram 120 for the normally closed reclosers 24, 30and 32 showing the six possible states that they can be in at anyparticular point in time based on the discussion herein. These statesinclude a “normal” state at oval 122 where the recloser 24, 30 or 32 isclosed, a “wait for voltage” state at oval 124 where the recloser 24, 30or 32 is open and the run timer is off, a “fast close/open” state atoval 126 where the recloser 24, 30 or 32 is closed and the run timer ison, a “wait for test” state at oval 128 where the recloser 24, 30 or 32is open and the arm pulse is off, a “lockout” state at oval 130 wherethe recloser 24, 30 or 32 is open and the run timer is off, and a“testing” state at oval 132 where the recloser 24, 30 or 32 is closedand then opened.

Each state is running a loop sequence algorithm that makes sequentialand repeated determinations of whether the recloser 24, 30 or 32 shouldmove to another state or remain in the state it is in, where if acondition is true, the arrows from one state to another state indicatewhat state the recloser 24, 30 or 32 moves to. If the recloser 24, 30 or32 does transition to another state, then the process returns to thefirst determination when the recloser 24, 30 or 32 transitions back tothat state.

In the “normal” state 122 the recloser 24, 30 or 32 is closed. When therecloser 24, 30 or 32 is in the “normal” state 122 the algorithm firstdetermines if there is a voltage sag with the run timer off and, if so,turns the run timer on, but remains in the “normal” state represented byline 134. The algorithm then determines whether fault current has beendetected by the recloser 24, 30 or 32 for the TCC curve and delay timefor the recloser 24, 30 or 32, where, if so, moves the recloser 24, 30or 32 to the “wait for test” state 128 on line 136. If there is nodetected fault current, then the algorithm determines whether there isno voltage on both sides of the recloser 24, 30 or 32 and the run timerhas exceeded the pulse sequence time and, if so, moves the recloser 24,30 or 32 to the “wait for voltage” state 124 on line 138. If there isvoltage in the “normal” state 122, the algorithm then determines ifthere has been voltage for a certain period of time and, if so, turnsthe run timer off and the arm pulse off and stays in the “normal” state122 on line 140. The algorithm then determines if there has been faultcurrent for the TCC time with the run timer on and, if so, sets the armpulse, and stays in the “normal” state 122 on line 142.

In the “wait for voltage” state 124 the recloser 24, 30 or 32 is open.When the recloser 24, 30 or 32 is in the “wait for voltage” state 124,the algorithm first determines if there has been no voltage sag for acertain period of time and, if so, returns to the “normal” state 122 online 144. If there is or has been a voltage sag, then the algorithmdetermines whether there has been a good voltage for a predeterminedperiod of time, such as two seconds, and the arm pulse is on and, if so,moves the recloser 24, 30 or 32 to the “wait for test” state 128 on line146. If there is no voltage sag, then the algorithm determines whetherthere has been a good voltage for two seconds and the arm pulse is offand, if so, moves the recloser 24, 30 or 32 to the “fast close/open”state 126 on line 148.

In the “fast close/open” state 126 the recloser 24, 30 or 32 closes thenopens quickly. When the recloser 24, 30 or 32 is in the “fastclose/open” state 126, the algorithm first determines if fault currentis present while the recloser 24, 30 or 32 is closed and, if so, movesthe recloser 24, 30 or 32 to the “wait for test” state 128 on line 150.If this is not occurring, the algorithm then determines that no faultcurrent is present and the fast close/open is done and, if so, moves therecloser 24, 30 or 32 to the “normal” state 122 on line 152.

In the “wait for test” state 128 the recloser 24, 30 or 32 is open. Whenthe recloser 24, 30 or 32 is in the “wait for test” state 128, thealgorithm first determines if the run timer is equal to pulse 1, 2, 3 or4 and, if so, moves the recloser 24, 30 or 32 to the “testing” state 132on line 154. If the run timer is not equal to 1, 2, 3 or 4, thealgorithm determines if the run timer is done and, if so, moves therecloser 24, 30 or 32 to the “lockout” state 130 on line 156. Also, ifboth sides of the recloser 24, 30 or 32 are at zero voltage, then therecloser 24, 30 or 32 moves to the “wait for voltage” state 124 on line160.

In the “lockout” state 130 the recloser 24, 30 or 32 is open. When therecloser 24, 30 or 32 is in the “lockout” state 130, the algorithmdetermines if there is a reset of the recloser 24, 30 or 32 and, if so,moves the recloser 24, 30 or 32 to the “fast close/open” state 126 online 158.

In the “testing” state 132 the recloser 24, 30 or 32 first closes thenquickly opens, or pulses the recloser 24, 30 or 32. When the recloser24, 30 or 32 is in the “testing” state 132, the algorithm firstdetermines if while the recloser 24, 30 or 32 is closed fault current isstill being detected and, if so, moves the recloser 24, 30 or 32 back tothe “wait for test” state 128 on line 166. If the fault current is notdetected while the recloser 24, 30 or 32 is closed, the algorithmdetermines that the fault is cleared and moves the recloser 24, 30 or 32to the “normal” state 122 on line 162.

FIG. 5 is a state diagram 170 for the normally open reclosers 26 and 28,which have five states that they can be in at any particular point intime based on the discussion above. These states include the “normalstate” at oval 172 where the recloser 26 or 28 is open, a “locked open”state at oval 174 where the recloser 26 or 28 is open and the run timeris off, a “locked closed” state at oval 176 where the recloser 26 or 28is closed and the run timer is off, a “testing” state at oval 178 wherethe recloser 26 or 28 is closed then opened after an arm pulse, and the“wait for test” state at oval 180 where the recloser 26 or 28 is openand the run timer is on.

In the “normal” state 172 the recloser 26 or 28 is open. When therecloser 26 or 28 is in the “normal” state 172, the algorithm firstdetermines whether there is voltage sag and, if so, moves the recloser26 or 28 to the “wait for test” state 180 on line 182. If there is novoltage sag for 200 ms and the run timer is off, the algorithm maintainsthe recloser 26 or 28 in the “normal” state 172 on line 184.

In the “locked open” state 174 the recloser 26 or 28 closes then quicklyopens. When the recloser 26 or 28 is in the “locked open” state 174, aforced reset of the recloser 26 or 28 returns the recloser 26 or 28 tothe “normal” state 172 on line 186.

In the “locked closed” state 176 the recloser 26 or 28 is closed. Whenthe recloser 26 or 28 is in the “locked closed” state 176, the algorithmfirst determines if fault current is present and the recloser 26 or 28has reached its TCC curve and the arm pulse is complete and, if so,moves the recloser 26 or 28 to the “wait for test” state 180 on line188. If this is not occurring, the recloser 26 or 28 can be manuallyreset back to the “normal” state 172 on line 190.

In the “testing” state 178 the recloser 26 or 28 closes then quicklyopens. When the recloser 26 or 28 is in the “testing” state 178, thealgorithm first determines if the run timer has reached the last pulseand there is fault current and, if so, moves the recloser 26 or 28 tothe “locked open” state 174 on line 192. If these decisions are notoccurring, the algorithm then determines if there is fault current and,if so, moves the recloser 26 or 28 to the “wait for test” state 180 online 194. If there is no fault current, then the algorithm moves therecloser 26 or 28 to the “locked closed” state 176 on line 196.

In the “wait for test” state 180 the recloser 26 or 28 is open. When therecloser 26 or 28 is in the “wait for test” state 180, the algorithmfirst determines if the run timer is equal to the arm pulse times andthe arm tests are complete and, if so, moves the recloser 26 or 28 tothe “testing” state 178 on line 198. If there is no voltage sag for 500ms, the algorithm moves the recloser 26 or 28 to the “normal” state 172on line 200.

FIG. 6 is a state diagram 210 for the switches 34-52, which have fivestates that it can be in at any particular point in time. These statesinclude the “normal” state at oval 212 where the switch 34-52 is closed,a “locked open” state at oval 214 where the switch 34-52 is open and therun timer is off, an “armed” state at oval 216 where the switch 34-52 isclosed and is ready to count pulses, a “decision” state at oval 218where the switch 34-52 is closed and is determining whether it shouldopen when its value is reached, and an “active test” state at oval 220where the switch 34-52 is closed and is counting pulses.

In the “normal” state 212 the switch 34-52 is closed. When the switch34-52 is in the “normal” state 212, the algorithm first determines ifthere is voltage sag and the run timer is off and, if so, turns the runtimer on and maintains the “normal” state on line 222. If the run timeris on, the algorithm determines if fault current is present and, if so,moves the switch 34-52 to the “armed” state 226 on line 224.

In the “locked open” state 214 the switch 34-52 is open. When the switch34-52 is in the “locked open” state 214, the switch 34-52 can bemanually reset and the run timer turned on and the switch 34-52 isreturned to the “normal” state 212 on line 226.

In the “decision” state 216 the switch 34-52 is closed. When the switch34-52 is in the “decision” state 216, the algorithm determines if thefirst position value matches the pulse number and the process is in thefirst set of pulses, and the condition is true causing the algorithm tomove the switch 34-52 to the “locked open” state 214 on line 228. Or,when the second position value matches the pulse number and the processis in the second set of pulses, the condition is also true and thealgorithm moves the switch 34-52 to the “locked open” state 214 on theline 228. Finally, when the third position value matches the pulsenumber and the process is in the third set of pulses, the condition isalso true and the algorithm moves the switch 34-52 to the “locked open”state 214 on the line 228. If the condition is not true, the algorithmmoves the switch 34-52 back to the “armed” state 218 on line 230.

In the “armed” state 218 the switch 34-52 is closed. When the switch34-52 is in the “armed” state 218, the algorithm determines if the resettimer has elapsed or there is no voltage sag and, if so, the algorithmmoves the switch 34-52 back to the “normal” state 212 on line 232. Thealgorithm then determines if there is a possible test and, if so, movesthe switch 34-52 to the “active test” state 220 on line 234.

In the “active test” state 220 the switch 34-52 is closed. When theswitch 34-52 is in the “active test” state 220, the algorithm firstdetermines if there is no voltage sag and, if so, moves the switch 34-52to the “normal” state 212 on line 236. If there is voltage sag, thealgorithm waits for a 500 ms delay to see if the voltage sag remainsand, if so, moves the switch 34-52 to the “decision” state 216 on line238.

In the first embodiment referred to above, the reclosers 24, 30 and 32are coordinated using suitable TCC curves so that the recloser 32 opensbefore the recloser 30 and the recloser 30 opens before the recloser 24.For example, the recloser 24 may have a TCC delay value of 4, therecloser 30 may have a TCC delay value of 3 and the recloser 32 may havea TCC delay value of 2. The recloser is 26 coordinated with a firstdelay and a TCC curve that is faster than the TCC curve of the recloser32, for example, a TCC delay value of 1, so that it will perform faulttesting after the reclosers 24, 30 and 32 have had time to perform a setof fault testing pulses. The recloser 28 is coordinated with a seconddelay that is longer than the first delay and a TCC curve that is thesame as the TCC curve of the recloser 26 so that it will perform faulttesting after the recloser 26.

All of the reclosers 24-32 are in the “normal” states 122 or 172 if nofault current or voltage sag is detected. If a fault occurs in, forexample, the feeder segment 70, fault current will run along the faultpath from the source 12, through the recloser 24, through the switches34 and 36 and into the fault. All of the downstream switches 38-52 andthe reclosers 26, 28, 30 and 32 from the segment 70 do not see the faultcurrent, but experience loss of voltage. All of the reclosers 24-32 andall of the switches 38-52 first start the run timer when they detect alarge enough voltage drop. The reclosers 26 and 28 will detect voltagesag and move to the “wait for test” state 180 and remain open. Inresponse to detecting the fault current, when the slower TCC value ofthe recloser 24 is reached it will also move to the “wait for test”state 128 and will open, which removes power from the feeders 18 and 20because the reclosers 26 and 28 are also open. The switches 34 and 36also detect the fault current and move to the “armed” state 218. Therecloser 24 will then move to the “testing” state 132 for testing todetermine if the fault is still present, and then return back to the“wait for test” state 128. When the recloser 24 is tested, the switches34 and 36 move to the “active test” state 220. If the fault is notpresent, the reclosers 24-32 and the switches 34-52 all return to the“normal” states 122, 172 and 212. In response to detecting the originalfault current and being armed, and then detecting the fault currentagain during the testing, the switches 34 and 36 will move to the“decision” state 216 to increment their counter to 1 and determine iftheir count value has been reached and, if not, return to the “armed”state 218. The recloser 24 then will go back to the “testing” state 132for a second time and if the fault current is still present, and theswitches 34 and 36 will again move to the “active test” state 220 andthe “decision” state 216. Since the switch 34 is assigned value 3 forthe power source 12, it remains closed and armed. However, since theswitch 36 is assigned value 2 for the power source 12 it will move tothe “locked open” state 214 and the recloser 24 will return to the“normal” state 122 and stay closed since the fault current has beenremoved by the switch 36 after being opened, and thus power will beprovided to feeder segments 66 and 68 from the source 12.

Once the segment 70 has been isolated from the source 12 from the openswitch 36, all of the segments 72-90 downstream of the segment 70 arealso isolated and not receiving power. The power restoration system thenproceeds to isolate the segment 70 at its downstream side and providepower to the downstream segments 72-90 from the segment 70. When theswitch 36 opens, and a certain run time has elapsed, the reclosers 30and 32 will move to the “wait for voltage” state 124 and open becausethey have not seen any voltage on both sides of the reclosers 30 and 32,and will stay in that state until voltage is restored. As mentionedabove, the reclosers 24 and 26 are coordinated with a delay so that thereclosers 26 and 28 do not operate until after the reclosers 24, 30 and32 go through their fault interrupting operation, where the recloser 26operates on a run time delay that is shorter than the run time delaythat the recloser 28 operates on.

When the delay time of the recloser 26 elapses and the recloser 26 doesnot see any voltage at its formerly upstream side, it will move to the“locked closed” state 176. When the recloser 26 closes power is restoredto the segments 82, 84, 86 and 88 from the power source 14. When therecloser 32 detects voltage at it formerly downstream side, but nowupstream side, it will go into the “fast close/open” state 126 to testand detect fault current, and since no fault current is present, therecloser 32 will move to the “normal” closed state 122, and power willbe restored to the segments 74, 76, 78, 80 and 90. Also, the recloser 28no longer detects a voltage sag and moves back to the “normal” openstate 172. When the recloser 30 is in the “wait for voltage” state 124and the recloser 32 closes, the recloser 30 detects voltage at itformerly downstream side, but now upstream side, and it will also gointo the “fast close/open” state 126 to test and look for fault current.However, in this case the recloser 30 detects fault current from thefault in the segment 70, and will move to the “wait for test” state 128and then perform the testing between the “wait for test” state 128 and“testing” state 132 and the switch 38 will be armed and move between the“active test” state 220 and the “decision” state 216 during the testing,as described. The counter value of the switch 38 for the source 14 is 3,so that when the testing causes the switch 38 to reach this value, itwill move to the “locked open” state 214 to completely isolate the faultin the segment 70, and the recloser 30 will move to the “normal” state122, where power is restored to the segment 72 from the source 14. Inthis configuration, the smallest possible section of the feeder 18 iswithout power, only in the segment 70, and no communication was requiredbetween the switches 34-52 and the reclosers 24-32 to accomplish that.Once the fault is found and the damage repaired, the switches 36 and 38are manually closed and their run timers are reset to return to the“normal” state 212. The recloser 26 is then reset and returns to the“normal” state 122.

With the network 10 in the fault isolation configuration as describedbefore the damage is repaired, another fault could occur in the feeder18 or 20 that also needs to be isolated. For example, a fault may occurin the segment 90, where the recloser 26 would open in response to thefault because it has a shorter TCC value than the recloser 32, and thereclosers 26 and 28 would move to the “wait for test” state 128 becauseof the voltage sag to perform testing, where power is removed from thesegments 72-90. Also, the switches 42-52 move to the “armed” state 218.With no voltage on either side, the reclosers 30 and 32 open and move tothe “wait for voltage” state 124. The recloser 26 moves to the “fastclose/open” state 126 for testing and sees no fault current, and thusmoves to the “locked closed” state 176, which causes the switches 46, 48and 50 to return to the “normal” state 212 because they now receivevoltage from the source 14, and power is restored to the segments 82,84, 86 and 88. The recloser 32 has voltage on its upstream side from thepower source 14, and thus moves to the “fast/open close” state 126, the“wait for test” state 128 and the “testing” state 132 to performtesting, which causes the switch 52 to detect the testing and move fromthe “armed” state 218 to the “active test” state 220 to the “decision”state 216 and then to the “locked open” state 214 when its value of 1for the power source 14 is reached. The recloser 32 then does not detectthe fault current and moves to the “normal” closed state 122, whichrestores power to the segments 74, 76, 78 and 80, thus isolating thefault in the segment 90. The recloser 30 then detects that voltage hasbeen restored at its upstream side and moves to the “fast close/open”state 126 to perform testing, sees no fault current, and then moves tothe “normal” state 122, which restores power to the segment 72. Further,when the recloser 28 sees no voltage it moves to the “testing” state 178and then to the “locked open” state 174. FIG. 7 is the network 10 withthe switches 36, 38 and 52 open and the faults isolated in the segments70 and 90.

In the second embodiment referred to above, all of the reclosers 24-32have the same TCC value, for example, each has a TCC value of 2, whichmakes the power restoration system easier to set up than the firstembodiment in that each recloser 24-32 doesn't need as much timingcoordination with the other reclosers 24-32. The reclosers 26 and 28still have the same delay as discussed above before operating theirpower restoration process. Also, the state diagrams for the normallyopen reclosers 26 and 28 and the switches 34-52 for the secondembodiment are the same as the state diagrams 170 and 210, respectively.The state diagram for the normally closed reclosers 24, 30 and 32 forthe second embodiment is similar to the state diagram 140 for the firstembodiment and is shown in FIG. 8 as state diagram 250, where likeelements to the state diagram 140 are identified by the same referencenumber. The sixth and last operation that is performed at the “normal”state 122 is a reset on line 252 when the TCC curve is 1 and the armpulse is off. Further for the line 160, a delay is added based on theTCC curve selected.

In this embodiment, if there is a fault in the segment 78, the recloser24 detects the fault current and moves to the “wait for test” state 128and opens. The recloser 30 detects the fault current and moves to the“wait for test” state 128 and opens. Then, since there is no voltage oneither side, the recloser 30 moves to the “wait for voltage” state 124.The recloser 32 also detects no voltage on either side, moves to the“wait for voltage” state 124 and opens. The recloser 26 detects voltageonly on one side from the source 14, moves to the “wait for test” state180 and remains open. The recloser 28 detects voltage only on one sidefrom the source 16, moves to the “wait for test” state 180 and remainsopen. The switches 34, 36, 38, 40 and 42 also detect the fault currentand move to the “armed” state 212. The recloser 24 moves to the“testing” state 132 to perform testing and when the recloser 24 does notdetect fault current because the recloser 30 is open, it and theswitches 34, 36 and 38 will go back to the “normal” closed states 122and 212, thus restoring power to the segments 66, 68, 70 and 72. Withvoltage on one side, the recloser 30 will move to the “fast close/open”state 126 closing then opening to look for a continuing fault. Then therecloser 30 will perform testing by moving between the “wait for test”state 128 and the “testing” state 132. During the testing, the switch 42moves between the “active test” state 220 and the “decision” state 216and once it reaches its value for the source 12, as discussed above,will move to the “locked open” state 214. Also, the recloser 28 seesgood voltage on both sides and moves to the “normal” open state 172. Therecloser 30 will also not detect fault current anymore and move to its“normal” closed state 122, thus restoring power to the segments 74, 76and 90. The recloser 26 is still in the “wait for test” state 180 andperforms testing when its delay is reached at the “testing” state 178,doesn't detect fault current, and moves to the “locked closed” state176, thus restoring power to the segments 82, 84, 86 and 88. Therecloser 32 is still in the “wait for voltage” state 124, and whenvoltage is applied to the recloser 32 it moves to the “fast close/open”state 126 and detects fault current, then moves to the “wait for test”state 128. Testing occurs as the recloser 32 moves between the “wait fortest” state 128 and the “testing” state 132. During the testing, theswitch 44 moves between the “active test” state 220 and the “decision”state 216 and once it reaches its value for the source 14, as discussedabove, will move to the “locked open” state 214, thus restoring power tothe segment 80.

If a second fault occurs in the segment 90 as discussed with referenceto the first embodiment, the recloser 24 detects the fault current and,moves to the “wait for test” state 128 and opens. The recloser 30detects the fault current and moves to the “wait for test” state 128 andopens, then when there is no voltage on either side moves to the “waitfor voltage” state 124. The recloser 28 detects voltage only on one sidefrom the source 16, moves to the “wait for test” state 180 and remainsopen. The switches 34, 36, 38, 40 and 52 also detect the fault currentand move to the “armed” state 218. The recloser 24 moves to the“testing” state 132 to perform testing and when the recloser 24 does notdetect fault current because the recloser 30 is open, it and theswitches 34, 36 and 38 will go back to the “normal” closed states 122and 172, thus restoring power to the segments 66, 68, 70 and 72. Therecloser 30 still detects fault current as it moves to the “fastclose/open” state 126, and then between the “wait for test” state 128and the “testing” state 132. During the testing, the switch 52 movesbetween the “active test” state 220 and the “decision” state 216 andonce it reaches its value for the source 12, as discussed above, willmove to the “locked open” state 214. The recloser 30 and the switch 40will not detect fault current anymore and move to their “normal” closedstate 122 and 172, thus restoring power to the segments 74, 76 and 90.The recloser 28 is still in the “wait for test” state 180 and performstesting between the “wait for test” state 180 and the “testing” state178, continues to detect fault current, and moves to the “locked open”state 174.

In the third embodiment referred to above, the power restoration systemuses a different set of TCC curves for the second fault so that only therecloser 24-32 closest to the second fault will open, which reduces themomentary power outages. For the network 10 shown in FIG. 1, each of thereclosers 24-32 is assigned a different TCC curve value depending onwhich direction the power flow is coming from much in the same way asthe switches 34-52 are assigned their value. For example, the recloser24 may be assigned the TCC code 311, the recloser 26 may be assigned theTCC code 131, the recloser 28 may be assigned the TCC code 112, therecloser 30 may be assigned the TCC code 211, and the recloser 32 may beassigned the TCC code 121, where the first value in the code is usedwhen current flow is coming to the recloser from the power source 12,the second value in the code is used when current flow is coming to therecloser from the power source 14, and the third value in the code isused when current flow is coming to the recloser from the power source16. Also, the state diagram for the normally closed reclosers 24, 30 and32 for the third embodiment is the same as for the second embodiment asshown in FIG. 8, and the state diagrams for normally open reclosers 26and 28 and the switches 34-52 is the same as for the first embodiment asshown in FIGS. 4 and 5, respectively.

If a fault occurs in the segment 70 as discussed above for the firstembodiment, the procedure for opening the switches 36 and 38 to isolatethe fault in the segment 70 is the same as in the first embodiment,except the timing of the procedure is different for the recloser 24having the TCC value of 3, instead of 4, for current flow from thesource 12, where the isolation of the fault will occur quicker. Power isthen restored to the segments 72-90 from the power source 14 through therecloser 26, then after a short delay to the recloser 32, and then afteranother short delay to the recloser 30 causing fault current to flow inthe reclosers 30, 32 and 26, where they operate with the TCC values 1, 2and 3, respectively. Since the recloser 30 is the fastest it opens inreaction to the fault. The recloser 30 after detecting fault currentperforms testing between the “wait for test” state 128 and the “testing”state 132. The switch 38 moves between the “active test” state 220 andthe “decision” state 216, when the value of the switch 38 is reached itmoves to the “locked open” state 214 to isolate the fault in the segment70. Another test by the recloser 30 shows no fault and power is restoredto the segment 72, and thus all of the segments have power except thesegment 70 with the fault.

The foregoing discussion discloses and describes merely exemplaryembodiments of the present disclosure. One skilled in the art willreadily recognize from such discussion and from the accompanyingdrawings and claims that various changes, modifications and variationscan be made therein without departing from the spirit and scope of thedisclosure as defined in the following claims.

What is claimed is:
 1. A power restoration system for an electricalpower distribution network, the system comprising: at least one feeder;a plurality of power sources available to provide power to the at leastone feeder; a plurality of normally closed reclosing deviceselectrically coupled along the at least one feeder, each normally closedreclosing device including an interrupter and one or more sensors formeasuring conditions on the feeder at both sides of the reclosingdevice, where each normally closed reclosing device detects a faultcondition based upon sensor data and opens its interrupter in responseto the fault condition and where the normally closed reclosing devicesare coordinated with each other to open in response to the faultcondition depending on its location along the at least one feeder; and aplurality of normally closed switches electrically coupled along thefeeder between each adjacent pair of normally closed reclosing devices,each switch including one or more sensors for measuring conditions onone or both sides of the switch, each switch being assigned a positioncode having a value for each of the plurality of power sources thatdetermines when the switch will open in response to the fault conditionand which power source the switch is currently receiving power from,wherein timing control between the reclosing devices and the switchesallows the switch to be selectively opened to isolate the fault within asingle feeder section between each pair of adjacent switches or betweeneach switch and a reclosing device.
 2. The system according to claim 1wherein the number of switches between adjacent normally closedreclosing devices is three.
 3. The system according to claim 1 whereinthe plurality of power sources include a first power source at one endof the at least one feeder and a second power source at an opposite endof the at least one feeder, the system further comprising a firstnormally open reclosing device including an interrupter and one or morecurrent and voltage sensors for measuring current on the at least onefeeder and measuring voltage on the at least one feeder at both sides ofthe first normally open reclosing device, the first normally openreclosing device preventing power from the second power source to flowon the at least one feeder.
 4. The system according to claim 1 whereinthe plurality of normally closed reclosing devices are assigned a timecurve characteristic (TCC) value so that a first normally closedreclosing device downstream from one of the power sources has thelongest TCC value and a last normally closed reclosing device downstreamfrom the one power source has the shortest TCC value.
 5. The systemaccording to claim 1 wherein the plurality of normally closed reclosingdevices are assigned a same time curve characteristic (TCC) value. 6.The system according to claim 1 wherein the plurality of normally closedreclosing devices are assigned a time curve characteristic (TCC) codehaving a plurality of TCC values where a TCC value in the code sets theTCC value of the normally closed reclosing device depending on which ofthe plurality of power sources the normally closed reclosing device isreceiving power from.
 7. The system according to claim 1 wherein the atleast one feeder is two feeders including a main feeder having a powersource at each end and a branch feeder that is tapped off of the mainfeeder and has a power source at an opposite to the main feeder.
 8. Thesystem according to claim 1 wherein the at least one feeder is athree-phase feeder.
 9. A power restoration system for an electricalpower distribution network, the system comprising: a first feeder havinga first end and a second end; a first power source available to providepower to the first feeder at its first end; a second power sourceavailable to provide power to the first feeder at its second end; afirst normally closed reclosing device provided in the first feederadjacent to the first power source and allowing the first power sourceto provide power to the first feeder during normal operation; a firstnormally open reclosing device provided in the first feeder adjacent tothe second power source and allowing the second power source to providepower to the first feeder during power restoration conditions; a secondfeeder having a first end and a second end coupled to the first feeder;a third power source available to provide power to the second feeder atits first end; a second normally open reclosing device provided in thesecond feeder adjacent to the third power source and allowing the thirdpower source to provide power to the second feeder during powerrestoration conditions; at least second and third normally closedreclosing devices provided along the first feeder between the first andsecond normally closed reclosing devices and allowing the first powersource to provide power to the first feeder downstream of the normallyclosed reclosing device during normal operation, wherein each of thenormally closed and normally open reclosing devices includes aninterrupter and one or more current and voltage sensors for measuringcurrent on the feeder and measuring voltage on the feeder at both sidesof the reclosing device, where each normally closed reclosing devicedetects fault current and opens its interrupter in response to faultcurrent and where the normally closed reclosing devices are coordinatedwith each other to open in response to fault current depending on itslocation along the first feeder; and a plurality of normally closedswitches electrically coupled along the first and second feeders betweeneach adjacent pair of normally closed reclosing devices, each switchincluding one or more current and voltage sensors for measuring currenton the first or second feeder and measuring voltage on the first orsecond feeder at one or both sides of the switch, each switch beingassigned a position code having a value for each of the first, secondand third power sources that determines when the switch will open inresponse to the fault current and which power source the switch iscurrently receiving power from, wherein timing control between thereclosing devices and the switches allows the switch to be selectivelyopened to isolate the fault within a single feeder section between eachpair of adjacent switches or between each switch and a reclosing device.10. The system according to claim 9 wherein the number of switchesbetween adjacent reclosing devices is three.
 11. The system according toclaim 9 wherein the first, second and third normally closed reclosingdevices are assigned a time curve characteristic (TCC) value thatdetermines when the reclosing device performs fault testing so that thefirst normally closed reclosing device has a longer TCC value than thesecond normally closed reclosing device and the second normally closedreclosing device has a longer TCC value than the third normally closedreclosing device.
 12. The system according to claim 11 wherein the firstand second normally open reclosing devices have a TCC value that is thesame and is shorter than the TCC value of the third normally closedreclosing device.
 13. The system according to claim 11 wherein the firstand second normally open reclosing devices are assigned a delay so thatthey do not perform fault testing before the first, second and thirdnormally closed reclosing devices finish performing fault testing, andwherein the delay of the second normally open reclosing device is longerthan the delay of the first normally open reclosing device.
 14. Thesystem according to claim 9 wherein the first, second and third normallyclosed reclosing devices and the first and second normally openreclosing devices are assigned a same time curve characteristic (TCC)value that determines when the reclosing device performs fault testing.15. The system according to claim 14 wherein the first and secondnormally open reclosing devices are assigned a delay so that they do notperform fault testing before the first, second and third normally closedreclosing devices finish performing fault testing, and wherein the delayof the second normally open reclosing device is longer than the delay ofthe first normally open reclosing device.
 16. The system according toclaim 9 wherein the first, second and third normally closed reclosingdevices and the first and second normally open reclosing devices areassigned a time curve characteristic (TCC) code where a first TCC valuein the code sets the TCC value of the reclosing device when it isreceiving power from the first power source, a second TCC value in thecode sets the TCC value of the reclosing device when it is receivingpower from the second power source, and a third TCC value in the codesets the TCC value of the reclosing device when it is receiving powerfrom the third power source.
 17. A power restoration system for anelectrical power distribution network, the system comprising at leastone feeder, a plurality of power sources available to provide power tothe at least one feeder, a plurality of normally closed reclosingdevices electrically coupled along the at least one feeder, at least onenormally open recloser electrically coupled to the at least one feeder,and a plurality of normally closed switches electrically coupled alongthe at least one feeder between each adjacent pair of normally closedreclosing devices, each switch being assigned a position code having avalue for each of the plurality of power sources that determines whenthe switch will open in response to the fault current and which powersource the switch is currently receiving power from, wherein timingcontrol between the reclosing devices and the switches allows the switchto be selectively opened to isolate the fault within a single feedersection between each pair of adjacent switches or between each switchand a reclosing device.
 18. The system according to claim 17 wherein theplurality of normally closed reclosing devices are assigned a time curvecharacteristic (TCC) value so that a first normally closed reclosingdevice downstream from one of the power sources has the longest TCCvalue and a last normally closed reclosing device downstream from theone power source has the shortest TCC value.
 19. The system according toclaim 17 wherein the plurality of normally closed reclosing devices areassigned a same time curve characteristic (TCC) value.
 20. The systemaccording to claim 17 wherein the plurality of normally closed reclosingdevices are assigned a time curve characteristic (TCC) code having aplurality of TCC values where a TCC value in the code sets the TCC valueof the normally closed reclosing device depending on which of theplurality of power sources the normally closed reclosing device isreceiving power from.